The invention disclosed and claimed herein generally pertains to voice activity detection in a communication system. More particularly, the invention pertains to a voice activity detector which is of reduced complexity and does not require a multiplier. Even more particularly, the invention pertains to a voice activity detector for use with a transmitter disposed to transmit audio signals through an air interface, wherein transmissions are to be discontinued whenever speech is absent from the signal.
There is increasing interest in providing mobile phones and other small electronic devices with the capability to connect and communicate wirelessly, over short ranges, with one another. Such capability would eliminate or substantially reduce the need for cables between devices such as phones, PC cards, headsets and laptop computers. Moreover, a number of such devices could thereby be joined together, very readily, to form small networks. As an example of this interest, the assignee herein, a major supplier of mobile telecommunication equipment and systems, has initiated a program known as the Bluetooth air interface to develop wireless communication capability of the above type.
In interconnecting small devices over a short range air interface, it is very important to limit costs, and also to reduce overall interference levels on the interface. Accordingly, in an air interface such as the Bluetooth interface, a transmitter disposed to receive speech is provided with a discontinuous transmission (DTX) capability, which causes the transmitter to be switched off during speech pauses. Such capability reduces cost, by minimizing transmitter power requirements, and also reduces signal interference level. However, the discontinuous transmission functionality requires a Voice Activity Detector (VAD) to continually determine whether or not an audio signal, applied or inputted to the transmitter, contains a speech component In the past, VAD dectectors could require voice or speech coders. As disclosed, for example, by U.S. Pat. No. 6,023,674, issued to one of the inventors herein, such coders may be very complex. Prior art VAD detectors could also require multiplier devices, as disclosed by U.S. Pat. No. 5,970,441, likewise issued to one of the inventors herein. It would be very desirable to provide a VAD for an air interface of the above type which is of substantially reduced complexity, and which does not need either a multiplier or a voice coder of the type described in the prior art.